The Duct System Resistance

Ducts can be developed with round or rectangular cross section. Radius elbows should preferably be at least 1.5 times the diameter of the pipe for round tubes, or the equivalent of a round pipe size in the case of rectangular air ducts. Accuracy in assessing resistance to air flow through the duct system is important in the selection of the blower for application in the systems of cable channels (Fig. 3-6).

Resistance should be as low as possible in the interests of economy, as underestimate the resistance will damage the fan in order to ensure the required volume of air. You should carefully review the drawings of the building taking into account the paid duct areas and gaps. Keep all channel runs as short as possible, taking into account that the air flow should be conducted both can be contacted directly from the source to the destination. Select the locations of channel sales for proper air distribution. The ducts must be provided crosssectional areas that will air on the corresponding speed. Moderate speed, should be used in all ventilation to avoid loss of energy and reduce noise. Below the speed more often used in schools, churches, theaters, etc. instead of factories and other places, where the noise level from the air flow is not objectionable.

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